Gauge for setting the pitch of



May 2, 1944. ROBY 2,348,095

GAUGE FOR SETTING THE PITCH OF PROPELLER BLADES Filed March 30, 1942 g INVENTOR. 5 i //0/wce Fab] 7 A TTORNE Y.

Patented May 2, 1944 GAUG ma sa'rrmo 'rrm rrrcn or rnornnnan nmnns Horace H. Roby, Wichita, Kama, assignor to Roby, "Inc- Wichita- Kanaf, a corporation of Kansas Application March 30. 1942, Serial No. 436,900

S -Claims. (on. 33-1-14) I My invention; relates "to improvements. in gauges for setting the pitch of propeller blades. It'is necessary that the blades of a propeller have the proper pitch and that each-oithe blades have the same pitch. In variable pitch propellers, the blades must be checked-for trueness at regular intervals. f In setting the pitch of a propeller blade, it is customary to hold the gaugeagainst'the blade at .a selected distance from the center of the hub.

This distance is usually approximately two-thirds the distance from the center of the hub to the tip of the blade. A suitable-indicating means cooperating with a scale on the gauge permits a reading of the pitch angle of the blade to be taken. However, this reading is'not accurate unless the crank shaft on which the propeller is mounted is horizontal. When an airplane is resting on the ground, its crank shaft is tilted from the horizontal. Therefore, when measuring the pitch angle of the propeller blade, the angle at which the crank shaft is tilted must be taken into consideration. The usual practice is to dismount the entire propeller each time the pitch angle of the blades is measured.

An important object of my invention is to provide a novel propeller pitch gauge that permits the pitch angle of the propeller blades to be accurately determined without dismounting the propeller and regardless of the angle at which the fuselage and engine of the airplane are positioned.

Another object of my invention is the provision of a novel propeller pitch gauge that is selfclamping on the propeller blade thus leaving the mechanics hands free to make other adjustments and to record the data obtained.

Still another object of my invention is the provision of a propeller pitch gauge of the above mentioned character that is light in weight, simple in construction, andeflicient in operation.

Other objects and advantages of m invention will be apparent during the course of the following description.

In the drawing forming a part of this specification and wherein likenumerals are employed to designate like parts throughoutithe same,

Fig. 1 is a front elevation of a propeller pitch gauge embodying my invention;

Fig. 2 is a top plan view of the same, 1

Fig. 3 is an enlarged vertical sectional view taken on the line 33 of Fig. 1,

Fig. 4 is a fragmentary rear elevation of the gauge, and

Fig. 5 is a vertical sectional view, taken on the line H of Fig. 1.

In the companying drawing wherein is shown a preferred embodiment of my invention, the numeral ill designates a frame of sheet metal. The frame comprises an elongated base Illa and a laterally extending integral arm lllc.

The base Illa is formed with arectilinear edge lllb and the arm lOc terminates in an arcuate extension Id. The arcuateextensionllld par.- tially surrounds and rotatably retains a level protractor disk I I.

As best shown in Fig. 3, the front surface of the protractor disk II is maintained flush with the front surface of'the frame by a radial shoulder Ila. The protractor disk H is retained within the arcuate'cxtension llld by frictional engagement "of its periphery with the inner edge of the extension. A spirit level l2 mounted on the rearward side of the protractor. disk ll may, easily be seen-through an opening lib in the disk.

Indicatorma-rks i3 and M on the arcuate extension llldfco'operate with scales l5 and IS on the protractordisk H to indicate the number of degrees thatthe protractor disk is rotated either to the right or left of the initial position shown inFig. 1. Attention is directed to the fact that indicator mark [3 is disposed on a line which extends through the center of the protractor disk and is normal to the lower rectilinear edge lllb of the frame. The indicator mark it is disposed at an angle of degrees from indicator mark i3. Each of the. scales. I5 and I6 extends through degrees. Scale i5 extends in an anti-clockwise direction and the 180 mark registers withindicator mark it when the protractor disk isin'the initial position. Scale I 6 extends in a clockwise direction and the 0 mark registers with indicator mark It When the protractor disk is in the initial position. In other words, if the rectilinear edge llib of the frame is placed upon a horizontal surface and the pro.- tractor disk ll is in the initial position, the bubble in the spirit level I: will be visible and-centered.

A recess H in the upper edge of the frame is provided at its opposite ends with inclined surfaces i8 and Ill. As best shown in Fig. 1, the inclined surfaces l8 and I9 seat the leading and training edges of apropeller blade so that the chord of the blade is parallel to the rectilinear edge lllb. The inclined surface I8 and the lower edge of arm lllc provide a V- -shaped recess in which one edge of the propeller blade is retained. A clamp 20 slidable oh tfie end poriton of base llla overlies the oppositejedge of the propeller blade. andclamp 20 urges the clamp into engagement with thepropeller blade. As best shown in Fig. 1, the portion of the base Illa on which the clamp 20 slides is ofiset so that the clamp does not pro ject beyond rectilinear edge Mb.

When the pitch angle of a propeller blade is taken, the blade is rotated .to' a horizontal position and the gauge is clamped thereon, as shown in Fig. .1. The gauge may be applied to face either the butt or tip end of the blade. At the present time, most propeller blades are pm- A coil spring 2| confined'between' stop 22:

vided with a pitch line" which indicates the section of the blade at which the pitch angle is to be measured. The gauge is applied to the blade at the pitch line. If no pitch line is shown, the gauge is applied to each blade of-the propeller an equal distance from the center of the hub. As herelnabove described, this distance is usually approximately two thirds the distance from the center of the hub to the tip of the blades.

When the gauge is applied to the propeller blade, the protractor disk II is rotated until the spirit level I2 is horizontal. The indicator mark I! will indicate the pitch angle on outer scale- Ill. The angle indicated by the gauge will be the true pitch angle of the propeller blade if the crank shaft on which the propeller is mounted is horizontal. However, when the airplane is resting on the ground, the fuselage and engine are tilted. The angle at which the airplane is tilted varies with different types of planes. The crank shaft extends through the crank case. The bottom of the crank case is exposed or easily accessible and parallel with the crankshaft. Therefore, when the rectilinear edge lb of the pitch gauge is placed against the bottom of the crank case, the level protractor disk ll may be rotated to give the angle at which the crank case is tilted from the horizontal. The spirit level is rotated to a position above the opening lib and the reading taken on the inner scale I6 as .registered by indicator mark [4.

If the pitch angle of a right hand propeller blade is being measured, the number of degrees which the crank shaft is tilted from the horizontal plus the .number of degrees actually registered by the protractor when the pitch angle of the blade is measured will give the true pitch angle. If a left hand propeller blade is being measured, the number of degrees that the crank shaft is tilted from the horizontal must be subtracted from the measured pitch of the blade to give the true pitch angle. r

In variable pitch propellers my gauge may be usedto expeditiously give each blade the desired pitch. The operation is simple and mat be readily performed without dismounting the propeller. The angle of inclination of the crank shaft is measuredin the manner hereinabove described. The protractor disk is then rotated to add the number of degrees of desired pitch.

The gauge is then applied to the propeller blade and the blade rotated about its longitudinal axis:

until the spirit level I: is horizontal. The blade rotate the blade, loosen or tighten the clamps connecting the blade to the hub, and make other adjustments and perform other necessary operations.

The manner in which the gauge'grips the opposite longitudinal edges of the propeller blade so that the chord of the blade is parallel with the rectilinear edge lllb permits the 'gaugeto operate satisfactorily on eithera single cambered or a double cambered blade. Regardless of the regardless of the angle at which the fuselage and engine of the airplane are inclined from the horizontal. The clamp is self-retaining on the blade, thus leaving the hands of the mechanic free to perform other necessary operations.

' It is to be understood that the form of my invention herewith shown and described is,to be taken as a preferred example of the same and that various changes in the size, shape and arrangement of parts may be resorted to without departing from the spirit of my invention or the scope of the appended claims.

Having thus described my invention, I claim:

1. A propeller pitch gauge comprising a frame, self-adjusting means on said frame for releasably grippfiig the opposite edges of a propeller blade, and a level protractor rotatably mounted in the frame and adjustable with reference to the propeller blade to determine its pitch when the blade is in a horizontal position. a

2. A propeller pitch gauge comprising a frame having a base portion and a curved arm portion, self-adjusting means on the base portion of said frame for releasably gripping the opposite edges of a propeller blade, and a level protractor rotatably mounted in the curved arm portion of the frame, saidrprotractor in theform of a disk, said disk having graduations thereon cooperating with an indicator mark on the arm portion to register the pitch of the said propeller blade.

3. A propeller pitch gauge comprising a frame having a base portion and a curved arm portion, self-adjusting means on the base portion of said frame for releasably gripping the opposite edges of a propeller blade, and a level protractor rotatably mounted in the curved arm portion of the frame, said protractor in the form of a disk, said disk having graduations thereon cooperating with an indicator mark on the arm portion to register the pitch of thesaid propeller blade, said indicator mark'being on a line passing through the center of the disk and perpendicular to the chord of the propellerbiade.

4. A propellerpitch gauge comprising a frame having a curved arm portion and a base portion formed. with "a rectilinear, edge, self-adjusting means on, the; base of the frame for releasably gripping the leading and trailing edges of a propeller blade in a; manner to position the rectilinear edge of the frame. parallel to they chord of the blade,fiand.a'level protractor rotatably mounted in the curved'arm portion of the frame, said protractor] inltheform of a disk, said disk member havinggraduations thereon cooperating with an indicato nmark on the arm to register the pitch ofthe said propeller blade, said indicator mark being on a line passing through the center of the diskand normal tothe chord of the propeller bladeand' to the said rectilinear edge of the frame; g

,5. A- prcpelle'rpitch gauge comprising a frame having acurved arm portion and a base portion formed with a rectilinear edge, a stationary clamp I means on the base portion of the frame, a selfshape of the blade, the chord-of the air foil will plied to varying-types and shapes of propeller' The blade may be given the desiredblades. pitch quickly without dismounting the propeller adjusting clampmeans slidable on the frame, and a'level protrac'torrotatably mounted in the curved arm portion of the'frame, said protractor in the form of a disk, said disk member having graduations thereon cooperating with an indicator mark on the arm portion to register the pitch of the propeller blade, said indicator mark being on a line-passing through the center of the disk and normal to the'chord of the propeller blade and to the said rectilinear edge of the frame.

. HORACE H. ROBY. 

